What is near vertical incidence skywave (NVIS) propagation?
The correct answer is B: Short distance MF or HF propagation at high elevation angles. Near vertical incidence skywave (NVIS) propagation is short distance MF or HF propagation at high elevation angles. NVIS uses nearly vertical takeoff angles to reflect signals back down for short-range communications. For amateur radio operators, NVIS is useful for local/regional communications on lower bands. Understanding this helps when planning short-range HF communications.
Exam Tip
NVIS = short distance MF/HF at high elevation angles. Think 'N'VIS = 'N'early 'V'ertical 'I'ncidence 'S'hort distance. Short distance propagation using high takeoff angles (nearly vertical). Not near MUF, not long-path, not double-hop - just high-angle short-range.
Memory Aid
"NVIS = short distance MF/HF at high elevation angles. Think 'N'VIS = 'N'early 'V'ertical 'I'ncidence 'S'hort distance. Short distance propagation using high takeoff angles. Useful for local/regional communications on lower bands."
Real-World Application
You need to communicate 50-200 miles away on 40 meters. You use NVIS - a horizontal dipole low to the ground (high takeoff angle). The signal goes nearly straight up, reflects off the ionosphere, and comes back down for short-range coverage. NVIS is perfect for local/regional communications.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. NVIS isn't propagation near MUF - it's about takeoff angle, not frequency. NVIS can work at various frequencies.
Option C: Incorrect. NVIS isn't long-path propagation at sunrise/sunset - it's short-distance, high-angle propagation. Long-path is different.
Option D: Incorrect. NVIS isn't double-hop near LUF - it's single-hop, high-angle propagation. Double-hop and LUF aren't NVIS characteristics.
题目解析
The correct answer is B: Short distance MF or HF propagation at high elevation angles. Near vertical incidence skywave (NVIS) propagation is short distance MF or HF propagation at high elevation angles. NVIS uses nearly vertical takeoff angles to reflect signals back down for short-range communications. For amateur radio operators, NVIS is useful for local/regional communications on lower bands. Understanding this helps when planning short-range HF communications.
考试技巧
NVIS = short distance MF/HF at high elevation angles. Think 'N'VIS = 'N'early 'V'ertical 'I'ncidence 'S'hort distance. Short distance propagation using high takeoff angles (nearly vertical). Not near MUF, not long-path, not double-hop - just high-angle short-range.
记忆口诀
NVIS = short distance MF/HF at high elevation angles. Think 'N'VIS = 'N'early 'V'ertical 'I'ncidence 'S'hort distance. Short distance propagation using high takeoff angles. Useful for local/regional communications on lower bands.
实际应用示例
You need to communicate 50-200 miles away on 40 meters. You use NVIS - a horizontal dipole low to the ground (high takeoff angle). The signal goes nearly straight up, reflects off the ionosphere, and comes back down for short-range coverage. NVIS is perfect for local/regional communications.
错误选项分析
Option A: Incorrect. NVIS isn't propagation near MUF - it's about takeoff angle, not frequency. NVIS can work at various frequencies. Option C: Incorrect. NVIS isn't long-path propagation at sunrise/sunset - it's short-distance, high-angle propagation. Long-path is different. Option D: Incorrect. NVIS isn't double-hop near LUF - it's single-hop, high-angle propagation. Double-hop and LUF aren't NVIS characteristics.
知识点
NVIS, Near vertical incidence skywave, High elevation angles, Short distance propagation
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.